1. Field of the Invention
The present invention concerns a clamping device for securing a draw-in bolt on a machine table, a base plate, or the like, having a piston that is arranged axially displaceably in a recess of the machine table and is hydraulically actuable, and having a cover in order to close off the recess in the machine table, the piston and/or the cover forming a receptacle into which a draw-in bolt can be inserted through the cover and in which it can be secured by way of a clamping mechanism actuable by displacement of the piston.
2. Description of the Related Art
The machining of workpieces is often very complex, and can comprise a plurality of chip-generating and non-chip-generating operations on various machine tools in order o to produce the finished component from a blank. In all production sequences, it is essential that the workpiece assume a defined position on the particular machine tool for each operation.
For that purpose, it is usual in practical use first to clamp the workpiece that is to be machined onto a carrier pallet, and then to clamp the entire unit in place onto the respective machine tool by way of multiple draw-in bolts that are provided on the back side of the carrier pallet and are configured as centering elements, by inserting the drawing bolts into corresponding quick clamping units that are provided on the machine table. In this manner, it is possible during production to regard the position of the quick clamping devices as a fixed machine parameter, so that it is necessary only to position each workpiece precisely on the carrier pallet. The actual clamping and reclamping of the unit comprising the workpiece and carrier pallet onto the machines can then be accomplished very quickly and easily with no need for further positioning.
The known mechanical/hydraulic clamping devices from which the present invention proceeds are configured either as so-called surface-mount cylinders, which form closed units and can be clamped onto a machine table, a base plate, or the like (see DE 298 04 730 U1 or DE 298 11 699 U1); or as so-called flush-mount clamp closures, which can be countersunk into the machine tables, quick-closure plates, dies, etc. The known flush-mount clamp closures are inserted directly into a recess of the machine table or into a corresponding base element; a pressure chamber, which can be acted upon by a hydraulic medium in order to disengage the clamping device, is then formed between the piston of the closure and the recess of the machine table.
The use of such flush-mount clamp closures frequently proves problematic because the machine tables often do not possess the necessary casting quality, so that the receptacles cannot be produced with the requisite accuracy and sealing problems thus occur. In addition, the presence of cavities can in some cases greatly impair the service life of the pistons or the clamping devices or the service life of the seals. Moreover, the clamping forces are directed into the machine table, base element, or the like, so that distortion can occur therein.
Lastly, the recesses in the machine table must be machined with great accuracy in order to achieve correspondingly accurate positioning of the clamp closure.
It is therefore the object of the present invention to describe a clamping device of the kind cited initially, suitable for installation in a machine table or the like, which is configured in such a way that it can be installed easily in the machine table without the occurrence of sealing problems, and which is easy to maintain.
This object is achieved, in a clamping device of the kind cited initially, in that there is inserted into the machine table recess an integrally configured bushing in which the piston is held displaceably forming a pressure chamber, the cover being attached on the one hand to the bushing and on the other hand to the machine table, and the attachment to the machine table being accomplished by way of multiple bolts passing axially through the bushing, and the bushing and/or cover having centering surfaces for positioning on the machine table or the like.
Because the clamping device according to the present invention is configured a sealed unit, the sealing problems that arise with the existing art can be eliminated. The clamping device can furthermore be configured as a standardized compact component, so that manufacturing costs can be reduced. If positioning of the clamping device is accomplished by way of the cover, it is necessary only to provide corresponding centers on the machine table and on the cover, with the result that machining inaccuracies in the remaining region of the receptacle play only a limited role. Any annular gap that is possibly present between the receptacle and the bushing is sealed from below against oil or air by way of two O-rings.
The clamping device according to the present invention offers the further advantage that no distortions occur on the machine table during operation, since the clamping or disengagement forces are absorbed entirely within the clamping device. The service life of the clamping devices is moreover greatly increased because, for example, cavities in the machine table have no effect on the operation of the clamping device.
Centering of the cover on the machine table and of the bushing can be accomplished in a variety of ways. It has proven advantageous to provide on the cover a centering extension that engages into the bushing, a sealing element then advantageously being arranged between cover and bushing. For centering of the cover on the machine table, the outer rim of the cover can be configured as a centering rim which forms a fit with a depression provided on the machine table. The cover, in this context, can be countersunk into the machine table at least partially, but in particular completely so that it terminates flush with the table surface. The clamping device is advantageously supplied with a hydraulic medium and optionally with air in the bottom region of the bushing, since sealing between the bushing and receptacle can be most easily accomplished there.